Electrode rod holder  in a high-pressure discharge lamp

ABSTRACT

The invention relates to an improved electrode rod ( 1 ) holder with the aid of a metal tube piece  5  and a metal plate  6  connected in a fixed manner to the metal tube piece for a mercury ultra-high pressure discharge lamp.

TECHNICAL FIELD

This invention relates to high-pressure discharge lamps and specificallyto the problem of fastening an electrode rod.

PRIOR ART

High-pressure discharge lamps contain electrode rods in a dischargevessel, generally made from quartz glass, a discharge for lightgeneration being started and maintained between said electrode rods.Often, the electrode rods have thicker electrode heads. Such lamps areused not only for generating visible light, but for example also as UVemitters, which is also intended to be included below under the term“lamp”.

The electrode rods are held in discharge vessel end regions, which aregenerally referred to as “lamp stem” and contact is made with saidelectrode rods there. Among the many technical criteria involved in thedesign and production of high-pressure discharge lamps, until nowstability and reliability of the mechanical holding arrangement for anelectrode rod in the lamp stem has not played a significant role.

DESCRIPTION OF THE INVENTION

The present invention is based on the object of specifying ahigh-pressure discharge lamp and an associated production method with animproved electrode rod holding arrangement.

The invention provides a high-pressure discharge lamp with an electroderod, which is held in a glass vessel stem, characterized by a metal tubeportion, in which an electrode rod part is held and which is held in theglass vessel stem, the metal tube portion being fixedly connected to ametallic transverse support, which protrudes beyond the metal tubeportion transversely with respect to the direction of the electrode rod,

and a corresponding production method.

Preferred configurations are specified in the dependent claims and, inprecisely the same way as the description below with the variousfeatures, in principle relate to both categories of the invention,namely to the lamp as well as to the production method.

The basic concept of the invention consists in a metal tube portion formounting the electrode rod along a certain axial length. In contrast tothe flat (in the direction of the electrode rod axis) fastening plates,known from the prior art, the term “tube portion” is thereforeunderstood to mean that the tube portion has a markedly smaller wallthickness (transversely with respect to the electrode rod axis) thanaxial length. The axial length can, but does not have to be, longer thanthe outer diameter.

In addition, a transverse support for the tube portion is provided, i.e.a component part which is fixedly connected to the tube portion andprotrudes beyond said tube portion transversely with respect to thelongitudinal axis of the electrode rod and which produces or assists theanchoring of the tube portion in the lamp stem. This transverse supporttherefore to a certain extend acts as an anchor and can correspondinglybe designed in a wide variety of ways, for example as transverse rodswith a cross or star shape or else as plates corresponding to the priorart.

Preferably, the tube portion is round in just the same way as theelectrode rod, but other cross-sectional profiles are naturally alsoconceivable. Preferably, the cross-sectional profile of the tube portionis configured in such a way that the electrode rod fits in in such a wayas to substantially conform. However, this is not absolutely necessaryeither. Mechanical fixing can also be achieved with differentcross-sectional profiles, but this generally does not involve anyadvantages.

The mechanical support of the electrode rod along an axial extent isessential to the invention. That is to say that the inventors haveestablished that the conventional joints between electrode rods andfastening plates can result in problems in terms of reliability as aresult of the severe loading of the transition region between the twocomponent parts.

As is already known from the conventional plate fastenings, electricalcontact is preferably also made with the electrode rod via thefastening. The metal tube according to the invention is thereforepreferably electrically connected and at least partially conducts thelamp current.

A particularly preferred joining technique is provided by the rod beingpressed axially and cold into the tube portion. By dispensing with anexternal heating effect such as during soldering or welding,embrittlement of the metals involved, in particular of the electroderod, or another type of weakening as a result of high temperatures canbe avoided. With a corresponding fit, mechanically and electricallyeffective and permanent joints can be produced by virtue of thecompression.

In this case, the electrically effective contact areas can be enlarged,but also dimensional tolerances which are relevant for the mechanicalfit are compensated for by interposed foil portions. During theproduction, the tolerances can even be gauged individually and can betaken into consideration individually by virtue of foil portions beingprovided correspondingly in different numbers (or being omitted).

The use of a metal foil is also advantageous outside the tube portion,and not only therein. A foil can be placed or wound around the tubeportion according to the invention in order to alleviate or eliminateany stress and friction problems in relation to the surrounding glasswhich may occur primarily as a result of different coefficients ofthermal expansion.

A further improvement can be achieved with the invention by virtue ofthe fact that the electrode rod is tapered in the vicinity of the tubeportion according to the invention, but outside said tube portion. Inthis case, the tapering is intended in any case to be arranged closer tothe tube portion than to that end of the electrode rod which is on thedischarge side. The tapering serves the purpose of localizing andconcentrating bending movements in particular in the case of high-powerlamps with heavy electrode rods and/or electrode heads or else in thecase of electrode heads which are relatively solid in relation to theelectrode rods and the stability thereof in smaller lamps and lamps ofaverage size. By virtue of the arrangement outside the tube portion andtherefore outside the holding arrangement for the electrode rod, thereis less or no bending stress on the electrode rod part in the tubeportion and in particular less mechanical stress on glass parts whichsurround the tube portion or in which said tube portion is held.Instead, the electrode rod bends in a free region, in which there is nostress on any brittle glass parts.

In turn, the tube portion is preferably held in a glass cylinder, whichis arranged in the lamp bulb, as described above optionally with a metalfoil interposed, the glass cylinder being supported on the lamp bulb.The above-mentioned plate shape of the transverse support for the tubeportion is preferred. In this case, it is favorably provided at the endof the described glass cylinder and terminates said glass cylindertowards its end which is remote from the discharge, i.e. for its part issupported on the lamp bulb. The tube portion and the plate are in theprocess fixedly connected to one another, preferably produced from thesame material and, for example, welded, soldered or preferably producedin one piece.

The lamp current can be supplied from the outside in a manner known perse via metal foils, in particular molybdenum foils. Said foils can inprinciple be connected to the electrode rod itself, but also to the tubeportion according to the invention. Owing to the relatively large outercircumference of the plate, said foils are preferably attached thereto,with the result that the lamp current is passed from the foils, via theplate and the tube portion, to the electrode rod. Since the plate andthe electrode rod can touch one another, part of the lamp current cannaturally also flow past the tube portion.

A further improvement of the electrode rod holding arrangement can beachieved by the electrode rod being thickened at its end remote from thedischarge. Thus, an axial shift in the tube portion in the directiontowards the discharge can be avoided because the thickened portion canbe supported on the tube portion and/or on the plate or anothertransverse support. In the case of axially effective forces of inertiaas a result of vibrations during transport or else in use, this may beof importance, in particular in the case of electrode heads which arerelatively large in relation to the electrode rod and/or high-powerlamps with correspondingly heavy electrode rods and heads.

Preferred materials are tungsten and molybdenum for the electrode rod,the plate and the tube portion according to the invention, and tungstenfor the electrode head itself. The abovementioned foils between theelectrode rod and the tube portion according to the invention, ifprovided, are preferably made from tantalum, but can also be made frommolybdenum or tungsten; the foils outside the tube portion and the foilsfor supplying power from the outside are made from molybdenum.

Particularly attractive possible applications for the invention, asalready variously indicated, are in particularly high-power lamps. Theseare preferably mercury discharge lamps with operating pressures of 5 baror more and/or powers of over 1 kW, 2 kW, 3 kW, 4 kW and 5 kW, in orderof increasing preference.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be explained below with reference to a preferredexemplary embodiment, wherein the individual features may also beessential to the invention in other combinations and relate both to thelamp and to the production method.

The FIGURE shows a schematic and partially sectional vertical plan viewof part of an ultra-high-pressure discharge lamp according to theinvention as the exemplary embodiment.

PREFERRED EMBODIMENT OF THE INVENTION

The FIGURE shows a vertical electrode rod 1 consisting of tungsten withan electrode head 2 which is configured to be relatively solid. Theelectrode rod 1 and the electrode head 2 together form the cathode ofthe lamp and have a total mass of the order of magnitude of 0.3 kg. Theanode, which is not illustrated in the FIGURE apart from a relativelylarge electrode rod and an electrode head with a slightly deviatingshape, but has a similar construction, has a total mass of the order ofmagnitude of 1 kg.

This lamp is an industrial UV lamp for semiconductor lithography orlight exposure applications in LCD screen manufacture with a power ofthe order of magnitude of from 20 to 25 kW and a hollow lamp bulb 3(only partially illustrated in the FIGURE) with the size approximatelyof a football.

The lamp bulb 3 merges with a hollow-cylindrical bulb stem 4, whichactually reaches further downwards vertically than specified in theFIGURE. The lamp bulb 3 is therefore illustrated in full at the top andcut off at the bottom.

The electrode rod 1 is held in a molybdenum tube portion 5, whichmerges, in its region remote from the discharge, with a molybdenum plate6, which is supported on the inner wall of the bulb stem 4. The tubeportion 5 and the plate 6 are designed to be in one piece.

In this case, the electrode rod 1 has been pressed into the tube portion5 in the axial direction prior to fitting of the electrode head 2,wherein an individual number of tantalum foil portions has beeninterposed depending on the dimensional tolerances in the individualcase. These foil portions improve the mechanical fit and enlarge theelectrical contact areas, but are not illustrated in any more detail inthe FIGURE.

However, the FIGURE shows, by virtue of a slightly thicker line,molybdenum foil windings 7 radially outside the tube portion 5 accordingto the invention and between said tube portion 5 and a quartz glasscylinder 8 surrounding said tube portion 5.

The electrode rod 1 is thicker at its lower end, i.e. the end remotefrom the discharge, and is therefore supported in the axial direction onthe plate 6 or on the tube portion 5, with the thickened portion beingdenoted by 9.

In addition, the FIGURE does not show that the molybdenum plate 6 isconnected to molybdenum foil portions in the form of power supply linesin a manner known per se on its outer circumference, said molybdenumfoil portions being passed outwards within the bulb stem 4 and outside aglass fill portion (likewise not shown) therein, and which form agas-tight, but electrically conductive connection solution. The foilportions are spot-welded with relatively small weld spots of the orderof magnitude of 0.5-1 mm in diameter. The spot-welding operations mean anegligible heat input and do not result in embrittlement. In principle,other welding processes would also be possible here, for exampleresistance welding.

Finally, the FIGURE shows a tapered portion 10 of the electrode rod 1virtually directly above that end of the tube portion 5 which faces thedischarge, said tapered portion acting as a bending point for transversemovements in particular as a result of the electrode head mass andprimarily being provided for preventing breakages of the quartz glasscylinder 8.

Moreover, the molybdenum and tungsten parts are connected and joined inthe region of the electrode rod holding arrangement without anyhigh-temperature steps and are therefore much more ductile, i.e. lesssusceptible to faults, than conventional lamps.

1. A high-pressure discharge lamp with an electrode rod (1), which isheld in a glass vessel stem (4), characterized by a metal tube portion(5), in which an electrode rod part is held and which is held in theglass vessel stem (4), the metal tube portion (5) being fixedlyconnected to a metallic transverse support (6), which protrudes beyondthe metal tube portion (5) transversely with respect to the direction ofthe electrode rod (1).
 2. The lamp as claimed in claim 1, in which theelectrode rod (1) is inserted axially into the tube portion (5) and inthe process is cold-compressed with the tube portion (5).
 3. The lamp asclaimed in claim 2, in which a metal foil is interposed between theelectrode rod (1) and the tube portion (5).
 4. The lamp as claimed inclaim 1, in which the tube portion (5) is surrounded by glass (8), and ametal foil (7) is interposed between the tube portion (5) and the glass(8).
 5. The lamp as claimed in claim 1, in which the electrode rod (1)is tapered outside the metal tube portion at a point (10) which, whenviewed in its axial direction, is less removed from the metal tubeportion (5) than from the discharge-side electrode end (2).
 6. The lampas claimed in claim 1, in which the transverse support is a metal plate(6), which is fixedly connected to that end of the tube portion (5)which is remote from the discharge.
 7. The lamp as claimed in claim 6,in which the plate (6) is terminated by a glass cylinder (8) around thetube portion (5) and is supported on a lamp bulb (3, 4) which surroundsthe glass cylinder (8) and the plate (6).
 8. The lamp as claimed inclaim 6, in which the plate (6) is connected to a metal foil, whichforms a power supply line to the plate (6) and via said plate to theelectrode rod (1).
 9. The lamp as claimed in claim 1, in which theelectrode rod (1) is thicker at the end (2) remote from the discharge.10. The lamp as claimed in claim 1, in which the electrode rod (1), thetube portion (5) and possibly the plate (6) are made from at least oneelement selected from the group consisting of molybdenum and tungsten,and possibly the metal foil (7) between the tube portion (5) and theglass (8) and possibly the metal foil in the form of a power supply lineto the plate (6) are made from molybdenum, and finally, possibly themetal foil between the electrode rod (1) and the tube portion (5) ismade from at least one element selected from the group consisting oftantalum, molybdenum and tungsten.
 11. The lamp as claimed in claim 1,which is in the form of a mercury discharge lamp with an operatingpressure of at least 5 bar.
 12. The lamp as claimed in claim 1 with anelectrical power of at least 1 kW.
 13. A method for producing ahigh-pressure discharge lamp, in which an electrode rod (1) is fastenedin a metal tube portion (5) and is thereby fastened in a glass vesselstem (4), the metal tube portion (5) being fixedly connected to ametallic transverse support (6), which protrudes beyond the metal tubeportion (5) transversely with respect to the direction of the electroderod (1).
 14. The method as claimed in claim 13, in which the electroderod (1) is pressed into the tube portion (5) axially under pressure andwithout any external heating and is thereby connected mechanically andelectrically to said tube portion.
 15. The method as claimed in claim13, in which a metal foil is interposed between the electrode rod (1)and the tube portion (5).
 16. (canceled)
 17. The lamp as claimed inclaim 7, in which the plate (6) is connected to a metal foil, whichforms a power supply line to the plate (6) and via said plate to theelectrode rod (1).